It has become increasingly common in connection with large tractors to employ means for changing the temperature of the air admitted to the tractor cab. Usually, this takes the form of some means for cooling the air. The provision of air conditioning for a tractor cab of a large tractor adds very little percentagewise to the total cost of the tractor and makes it possible for the operator to operate for much longer periods of time in dusty fields without undue discomfort because of the dust. Furthermore, in many agricultural areas, the temperatures during the year in which such tractors are being used is quite high and unless some means is provided for cooling the air, the interior of the tractor cab can become extremely warm.
A problem arises, however, in connection with air conditioning for such a tractor cab. As pointed out, a large amount of dust is being drawn into the air conditioning inlet, regardless of where this inlet is located. This dust accumulates on the upstream side of the filter and due to the vibration of the tractor, it tends to drop off. In the past, the filters have been located in compartments from which the filter can be rather readily drawn for cleaning purposes, but in which the dirt or other foreign matter dropping off the filter tends to accumulate where it is rather difficult to remove it. For this reason, where the filter has been located in the roof of the tractor, the roof ceiling has been provided with a trap door permitting the opening of the compartment from the bottom to remove the dust. The drawback to this arrangement is that the operator is usually beneath the door and when the door is opened, a large amount of dirt or other foreign matter drops down on the operator and into the interior of the cab.